Following up on #3231

- `SD_DETECT_PIN` replaces `SDCARDDETECT`
- `SD_DETECT_INVERTED` replaces `SDCARDDETECTINVERTED`
- Revise the description of `SD_DETECT_INVERTED`
- Add a note about the override of `SD_DETECT_INVERTED` in
`Conditionals.h`

- Rename the pin so it can be tested with `PIN_EXISTS`
- Fix some incorrect tests for `SDCARDDETECT`

For consistency with other pins, allowing use of `PIN_EXISTS` macro.

The encrot values are used in only one place, and don’t vary, so remove
redundant references.

Hopefully this is helpful to organization and future expansion….

Hopefully this is helpful to organization and future expansion….

Hopefully this is helpful to organization and future expansion….